<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 5.21.1

Error message:
Copia file lato remoto fallita.

Accesso alla memoria non valido.

Stack trace:
(00DE97CE) TTerminal::CopyToRemote
(00FD0EE2) C5412_3
(00FD2F4A) ____ExceptionHandler
(00FCFD04) __ExceptionHandler
(000879EF) ntdll.dll
(00073EE1) ntdll.dll.KiUserExceptionDispatcher
(00015BB8) TCustomScpExplorerForm::ExecutedFileChanged
(00076D09) TEditorManager::CheckFileChange
(00074AA9) TEditorManager::Check
(0001950D) TCustomScpExplorerForm::Idle
(0004CE77) TNonVisualDataModule::DoIdle
(0004CE34) TNonVisualDataModule::SessionIdleTimerTimer
(003C85A0) System::Classes::_18201
(00040109) USER32.dll
(000370C5) USER32.dll
(00034E35) USER32.dll
(00034BFB) USER32.dll.DispatchMessageW

The problem happens rarely. I cannot reproduce it.